This invention relates generally to a direct gas-fired Industrial, commercial, or related type of heater, or more specifically to a heater to be used for heating substantially sized buildings, such as may be used and applied in the foregoing manner. Furthermore, because of the precise control provided for the gas-fired heater of this invention, and through its assembly of various components furnishes a substantial volume in capacity of heat with reduced generation of carbon monoxide, the heater of this invention may further be used and applied for agricultural purposes, such as in barns, or other confinement buildings, such as for use for housing and raising swine, applied in poultry, production, or for keeping other livestock, and reduce the incidence of harm to such animals because of the high efficiency of operations of this heater, with reduced generation of deleterious gases. Thus, the heater of this invention also has field of use application for agricultural purposes, such as in a hog house or a poultry house, or the like. The invention herein described is not a heat exchanger per se, since the combustion of the gas after ignition takes place directly within the air stream being heated, and not by conduction, with the heated air being channeled directly for discharge into the housing space to be warmed.
The improvement of the invention is that it further adds to the efficiency of combustion within such heater so as to work more effectively and safely in producing the quantities of heated air that may be needed to heat an agricultural-type building with effectively decreasing the production of noxious gases and also adding to safety.
The heating equipment of this invention, in which the direct fire burner of a novel type is enclosed contains no flue and all of the bi-products of combustion are released directly into the heated air which is then directly discharged into the space being heated. Since one application of this type of heater is to employ the heater in a small enclosed space, such as a hog house or poultry house, it is important to reduce the creation and release of deleterious exhaust and other gases, either in the form of carbon monoxide or nitrogen dioxide, so that the air remains breathable by the farm animals and by the farmer working in such an enclosed space. Furthermore, since the heater of this invention can also be applied for horticultural purposes, this heater can be installed for precisely regulating the heat generated and needed for warming a greenhouse, or the like, during usage.
The improved heater of this design substantially reduces to a minimum the generation of these deleterious noxious gases resulting from combustion.
Direct fire gas heaters typically are constructed in a variety of configurations. In the majority of such heaters, as manufactured, the burner is arranged upstream of a fan which functions in the manner of a draw-through type of arrangement. A number of other manufacturers position their burners down stream of the fan or blower discharge in what is defined as a blow-through configuration. Examples of the various types of devices can be seen in U.S. Pat. Nos. 5,083,918, 4,929,541 and 4,993,944 all to Potter et al. and in U.S. Pat. No. 3,630,499 which are owned by a common assignee of the improved burner of the current design.
Other types of burner arrangements that exist in the prior art can readily been seen in the Ehrich U.S. Pat. No. 3,485,043, the Coppin et al. U.S. Pat. No. 4,573,907 and in the Childs, U.S. Pat. No. 3,993,449, as well as the Pillard U.S. Pat. No. 3,885,919. Furthermore the Canadian Pat. No. 560,916 to Kind, shows a form of a gas burner contained within a heating arrangement which incorporate the flame zone of a combustion chamber.
In addition, other burner assemblies are shown in prior U.S. Patents to Lewis, U.S. Pat. No. 4,523,905; Coppin, U.S. Pat. No. 4,869,665; and Kikutami et al. U.S. Pat. No. 4,610,626.
As is well known in the art, the performance characteristics of the burner necessarily determines the operational range of the heating equipment to gauge whether it is in compliance with various requirements of the American National Standards Institute (ANSI) governing the functioning of the direct gas-fired industrial heaters. The burner design for which patent protection is sought herein is utilized in the industrial heating appliance, more specifically, in an agricultural type use or other industrial or commercial heating appliance. Various standards establish the criteria for maximum amounts of bi-products of the combustion, such as carbon monoxide, carbon dioxide, nitrogen dioxide, and aldehydes which can be discharged into the heated air. Obviously, such controls are done for the purpose of regulating the air quality of the building in which the equipment is to be installed for the safety to the worker as well as others.
Generally the air flow through a heater of this type design, and the temperature rise that occurs for the air that is being heated, determines the heating capacity of the subject unit. The air flow is directly related to the fan selected, the motor horsepower of the unit driving the fan, and the static pressure on the system during functioning. The temperature rise is controlled by the gas flow delivered to the burner, at any given air flow rate for the capacity air that is been blown through the unit, as induced by the blower.
As previously explained, the ANSI standards generally provide for a minimum requirement that must be met by units of this design. These standards generally allow for specific maximum additive levels of four particular hi-products of combustion, as previously identified, that may be released from the heating unit of this type during functioning. The products of combustion as previously explained and their respective allowable levels are as follows:
carbon dioxide-4,000 parts per million (ppm); PA1 carbon monoxide-5 parts per million (ppm); PA1 nitrogen dioxide-0.50 parts per million (ppm); PA1 aliphatic aldehyde-1.0 parts per million (ppm);
As can be understood, these are extremely low levels and therefore it is very important that a burner of this design be efficiently and effectively designed for the purpose of minimizing the creation of these combustion by-products. These particular chemical compounds, which are generally recognized in the trade as undesirable by-products from the functioning of heating units of this type, and their gases of combustion are basically recognized as unwanted by-products, which, if they can be reduced to an absolute minimum, not only adds to the safety to all people or animals within the heated space but enhances the quality of operation of the heating unit. The unit of this particular invention has been designed to provide for a minimization of the output of these undesirable by-products through the uniquely enhanced design and particular characteristics and features constructed to improve the heater of this invention.
For example, it has been previously determined through testing that there are three major factors that effect the production of carbon monoxide within the combustion process. The quantity of air that is provided to support combustion must closely match what is needed. If too little air is allowed to mix with the gas within the burner/combustion chamber, incomplete combustion occurs and noxious gases escape into the heated area. The rise in the level of carbon monoxide can easily be measured in the discharge airstream. On the other hand, if too much combustion air is introduced, quenching of the flame can occur and this abrupt cooling also causes incomplete combustion. By controlling the volume of primary and secondary combustion air, it can be shown that the deterious combustion products can be minimized. Thus, an equilibrium point must be attained and the amount of air that flows into the burner assembly and around thee early portion of the flame must be limited within a narrow window to allow as much as needed but prevent excess flow from quenching the flame.
An additional factor which affects the development of carbon monoxide related to the quenching phenomena of the flame and is due to the abrupt cooling of the flame after it exits from the combustion zone. Excess air is generally always provided in warm air heater applications. From the preceeding paragraph, it is important that the excees air is bypassed around the combustion zone. If the velocity of the bypass air is too high or if the flow pattern of the bypass air is overly disruptive, the excess air could impinge or penetrate the flame tips that are extending beyond the combustion zone. This type of air impingement or penetration into the flame tips causes a quenching of the flame by its premature cooling below the reaction temperature which can significantly increase carbon monoxide. Thus, a similar equilibrium point must be maintained between the bypass excess air and the primary and secondary combustion air and, in addition, the air flow pattern of the bypass air should not be intrusive to the flame.
The third known factor which affects the development of carbon monoxide and to a significant degree nitrogen dioxide relates to flame impringement on the metal surfaces (wall, baffles or diverters) of the firebox. The flame impingement on the cooler metal surface sometimes present in turbulant flame patterns relates to the abrupt cooling phenomena which again results in the creation of carbon monoxide. Where flame impingement is allowed to occur on a more continuous basis, the metal surface will overheat creating hot spots which act to generate higher levels of nitrogen dioxide in the discharge air stream. Air flow barriers are provided which prevent flame impingement on the metal surfaces of this design in a manner so as not to overly cool the flame by this technique.
In atmospheric gas type burner applications, primary combustion air is premixed with the gas by the momentum of the jet of gas expelled by the gas orifice. The text on the subject of atmospheric burner design indicates the normal range for the percentage or primary air, as a percent of theoretical, mixing with the gas is between 35% and 65%. By locating the burner and combustion zone on the suction side of the fan (negative static pressure side in relationship to normal room pressure) while leaving the primary air intake at room pressure, the percentage of primary air, as a percent of theoretical that premixes with the gas within the confines of the burner, is increased significantly without experiencing the undesirable characteristic of flame lifting away from the outlet port. As a result, much less secondary combustion air is required to achieve complete combustion. With the requirement for less secondary air, baffling may be used to restrict the secondary air flow volume and velocity, such that the secondary air does not intrude into the inner cone of flame.
As can be understood from the above discussion, the manner in which air is introduced into the combution zone is just as important as how much air is provided to support combustion. In the design requirements of this appliance, one must also be concerned with the generation of undesirable combustion bi-products when the heater is operated for an extended period of time with the access door in the opened position. The air flow pattern is significantly different with the door open than with the access door closed. Design solutions were developed through imperical testing which minimized the creation of deleterious exhaust or other gases.